kapt is for Kotlin.
First, add:
annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
to your dependencies closure.
Then, upgrade android.arch.persistence.room:rxjava2 and android.arch.persistence.room:testing to 1.0.0 instead of 1.0.0-rc1.
ref: https://developer.android.com/jetpack/androidx/releases/room